When an electric or electronic product is used, a power is generally supplied through a commercial power source. However, if a power supply line is not connected or mobility should be ensured, a battery serving as an energy storage apparatus is charged and an electric product is used with the charged energy. In this case, the battery may be implemented as a lead storage battery, a secondary cell stack or the like.
The energy storage apparatus charges an energy by using an adaptor device which converts a commercial current into DC or through a terminal which supplies a DC power generated from a generator of a vehicle or a motorcycle, and the energy storage apparatus is used as a kind of power source in a place or position where charging is required.
Meanwhile, as attention is focused on environment-friendly energy, there have been proposed many products using a solar cell for generating a power by means of the photoelectric effect representing that charges generated by solar rays transfer by using P- and N-type semiconductors.
However, an existing energy storage apparatus is individualized for each kind of power and thus charged only by a specific power source, and also such an energy storage apparatus is designed to have a behavior characteristic in which charging is performed under only a specific operation condition. Therefore, the energy storage apparatus does not ensure versatile application if different kinds of power sources are used.
Further, in recent days in which outdoor living is propagated, an energy storage apparatus designed to use solar rays as a charging power source in the outside is more necessary. An existing charging device using a solar cell does not effectively reflect characteristics of the solar cell having a differential behavior characteristic according to temperature, environment, light intensity or the like. Moreover, since only a complicated algorithm for enhancing the efficiency of the solar cell is applied as disclosed in the Korean Unexamined Patent Publication No. 2007-0078092, the energy storage apparatus is uneconomical, and users may not easily use the energy storage apparatus.